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4013 Flip Flop Toggle Start up

Discussion in 'Electronic Basics' started by Up in Canada, Apr 21, 2005.

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  1. Up in Canada

    Up in Canada Guest

    Hello-

    I am using a 4013 as a toggle to control a LED.
    Simple school project.

    I have Qbar connected to Data, Q is to a small fet that turns on a LED.

    The clk input is connected to a MOM push button switch that grounds it
    out when pushed.
    I have RESET and SET at ground.


    It works great so far!!


    Now, how do I control the Startup condition?

    I need to have one that powers up with the Q high (led on)

    I also will use the other half of the 4013 in the same exact way,
    totally independent, but need this Q to startup LOW( that led off).


    Thanks.


    Alvin
     
  2. You probably should debounce that switch to
    derive one active clock edge per push.
    Build the following circuit with a 1N914 diode
    (or equivalent), a 100k resistor, and a 100 nF
    cap. Connec TrueBriefly to the SET or RESET
    input of each FF, as dictated by your requirement.

    VCC
    |
    ---
    ---
    |
    o---------TrueBriefly
    |
    o---.
    | |
    .-. -
    | | ^
    | | |
    '-' |
    o---'
    |
    ===
    GND

    (created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de)
    (View with a fixed-width font.)
    Welcome.
     
  3. Up in Canada

    Up in Canada Guest

    You probably should debounce that switch to
    Errrr.... how do you reccomend?


    Perfect, it works great!! Thank you, thank you thank you thank you
    thank you!
     
  4. One way is to use an RC lowpass filter to take
    out most of the bounce trash, and follow it with
    a device having input hysteresis to preclude any
    multiple transitions should the LPF output cross
    a single stationary threshold more than once per
    push or release of the switch.

    Another way is to use a form C switch and hook
    the NO and NC signals to the SET and RESET
    inputs of a flip-flop whose output is bounce free.
     
  5. Chris

    Chris Guest

    Hi, Alvin. I'm hearing that this is what you're doing with 1/2 of a
    4013 (view in fixed font or M$ Notepad):


    ` .-----------------------.
    ` | .---. |
    ` | | | |
    ` | | | |
    ` | === | |
    ` | GND | |
    ` | .------o------. |
    ` | | S | |
    ` '----o D Q o-----------> To LED Driver
    ` | | |
    ` T | | |
    ` --- | | |
    ` .----o o------o 1/2 4013 | |
    ` | |CLK | |
    ` | | | |
    ` === | Q'o----'
    ` GND | |
    ` | R |
    ` '------o------'
    ` |
    ` ===
    ` GND
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    The way to get it to start in a known state is to apply a momentary
    pulse to the SET or RESET pin (not both) at startup like this:

    ` .-----------------------.
    ` | .---. |
    ` | | | |
    ` | | | |
    ` | === | |
    ` | GND | |
    ` | .------o------. |
    ` | | R | |
    ` '----o D Q o-----------> To LED Driver
    ` | | |
    ` | | |
    ` | | |
    ` VCC o 1/2 4013 | |
    ` + |CLK | |
    ` | | | |
    ` .-. | Q'o----'
    ` 10K| | | |
    ` | | | S |
    ` '-' '------o------'
    ` | |
    ` o---------------'
    ` |
    ` ---
    ` ---
    ` .01uF |
    ` ===
    ` GND
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    The R-C will result in a brief (about 0.1 ms.) high pulse at the SET
    pin, which will result in the 4013 coming up with Q = 1.

    You've got a bit of a problem, though, with the clock input, at least
    the way you describe it. You're trying to create a toggle, or "T" F-F
    out of a D F-F. That means there can be one and only one clock
    transistion each time you press the button. CMOS inputs can be seen as
    very small (pF range) capacitive loads. Because of leakage current on
    your perfboard or imperfections in the chip, your input seems to want
    to float high. When you press the button, you're discharging that
    small capacitor, leading to what seems to be a good single logic
    transistion.

    That's not a good idea for a couple of reasons. CMOS inputs aren't
    like TTL inputs, where they just naturally go to onoe logic state. And
    also, it's very bad practice to allow slow transistions on clock
    signals unless they're going into a schmitt trigger or something else
    that will shape them up. Strange things happen inside clocked logic
    ICs when the clock transition is pokey, and none of them are good.
    Possibly you're the beneficiary of beginners' luck.

    Anyway, the other half of the 4013 can help you with your issue here.
    If you've got a SPDT pushbutton, you could try this with the other half
    of the IC (view in fixed font or M$ Notepad):

    ` .--o-----------.
    ` | | |
    ` | .-. |
    ` | | | |
    ` | | | |
    ` | '-' |
    ` | | .------o------.
    ` VCC | === | S | Debounced
    ` + | GND.--o D Q o-------->
    ` | | | | | Clock Signal
    ` | o-' | | |
    ` '----o--__ | | |
    ` o-. o--o 1/2 4013 |
    ` | | |CLK |
    ` | | | |
    ` | | | Q'o
    ` | === | |
    ` | GND | R |
    ` | '------o------'
    ` '--o-----------'
    ` |
    ` .-.
    ` | |
    ` | |
    ` '-'
    ` |
    ` ===
    ` GND
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    (Note that we're're following one of the primary rules of CMOS, which
    is to never leave any input floating. Even if it isn't doing anything,
    the intermediate logic level at the input almost always dramatically
    increases power dissipation.)

    The SPDT pushbutton is normally asserting the RESET input high. When
    you press the button, it will let go of RESET before it asserts SET,
    and you won't have to worry about pushbutton bounce causing multiple
    clock transistions. When you let go of the pushbutton, SET will be let
    go, but the Q output will remain high until the first contact of the
    switch with the RESET input. This is called debouncing. One and only
    one logic transition.

    So, your whole one IC debounced toggle flip-flop should look something
    like this:

    ` .--o-----------. .---------------------.
    ` | | | | .---. |
    ` | .-. | | | | |
    ` | | |10K | | | | |
    ` | | | | | === | |
    ` | '-' | | GND | |
    ` | | .------o------. | .------o------. |
    ` VCC | === | S | | | R | |
    ` + | GND.--o D Q o--------. '---o D Q o------>
    ` | | | | | | | | |
    ` | o-' | | | | | | |
    ` '--o--__ | | | | | | |
    ` o-. o--o 1/2 4013 | VCC'-----o 1/2 4013 | |
    ` | | |CLK | + |CLK | |
    ` | | | | | | | |
    ` | | | Q'o .-. | Q'o---'
    ` | === | | 10K| | | |
    ` | GND | R | | | | S |
    ` | '------o------' '-' '------o------'
    ` '--o-----------' | |
    ` | o--------------'
    ` .-. |
    ` | |10K ---
    ` | | ---
    ` '-' 01uF |
    ` | ===
    ` === GND
    ` GND
    created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

    You can put your R-C pulse at the SET or RESET pin of the 2nd 1/2 of
    the 4013, depending on what you've got at the output, and whether you
    need it to power up ON or OFF. You will also have one and only one
    logic transition for every press of the pushbutton.

    Good luck with your homework
    Chris
     
  6. Up in Canada

    Up in Canada Guest

    Wow, thanks!!


    My switch actually *has* to be a momentary mini toggle, ie, the spring
    loaded ones that return to their original position.
    I'll go looking to make sure they make these in SPDT!!!

    Thank you, I really do appreciate your help. I looked in my textbooks
    first.

    Thanks!
     
  7. Up in Canada

    Up in Canada Guest

    Thank you too!!
     
  8. Up in Canada

    Up in Canada Guest

    one thing more.

    I may need to add more momentary switches in parallel for remote
    operation. Well not remote, but think of a light switch on each side of
    a room.
    It still has to be momentary toggles.

    Uh oh, I think it just got more complicated. I have to use the least
    amount of wires.

    Anyway to have a debounce with just the momentary spst? If I have to
    use a remote box with cable conected to mulitple leds, the less wiring
    in cables the better. If I have to do 30 leds you can see what I mean.
    I

    I'll reread it all before I post again.

    Thanks
    The excitement!!
     
  9. Here is a circuit which was once published in EDN, IIRC.
    It relies on positive feedback thru the series RC pair to
    effect a short duration threshold shift that suffices to avoid
    bounce effects for normal switch bounce.


    VCC
    | ___ ||
    .-. .-|___|--||---.
    | | | || |
    10k| | | 20k 100 nF |
    '-' | |
    | ___ | |\ |
    o-|___|--o-| >---------o--Debounced
    | |/
    | 20k
    | o
    |=|>
    | o
    |
    GND
    (created by AACircuit v1.28.4 beta 13/12/04 www.tech-chat.de)

    You can buy buffers with input hysteresis, so this approach
    makes the most sense when you just want one or two of
    these inputs and have leftover gates or PLD pins to use.
    That is a disadvantage, alright. That's why I mentioned
    the LPF and hysteresis (aka "Schmidt trigger") approach.
    ....
    Welcome.
     
  10. Chris

    Chris Guest

    No problemo. Some of this probably wouldn't have been in your
    textbook, anyway. The R-C pulse and the use of the forcing S and R
    inputs instead of D and CLK usually aren't in beginners digital logic
    books. There are a lot of "tricks" that will help you that they might
    not teach in class.

    For CMOS logic "tricks", try finding a copy of Don Lancaster's "CMOS
    COOKBOOK". If it's not at the library, you can get it from Amazon or
    Mr. Lancaster's website:

    http://www.tinaja.com/

    It's a good source for a lot of these tricks, and still very relevant
    to a lot of what you'll do with digital logic. Well worth it. I
    particularly like his discussion of MML (Mickey Mouse Logic) in Chapter
    3. It explains some of the limits of this stuff, which is easy to do
    with CMOS.

    Other sources of tricks are Mr. Lancaster's magazine columns (many of
    which are available on his website, too), and manufacturer data sheets
    and app notes. Look particularly at old National Semiconductor,
    Fairchild, and RCA COS-MOS appnotes if you can find them.

    Keep learning and having fun. It's not all in the textbooks.

    Chris
     
  11. Up in Canada

    Up in Canada Guest

    Larry,

    I will try that feedback approach.

    I will also research this schmidt trigger approach.

    Thank you!



    Chris,

    Thanks for the help and the references!!

    Thank you!
     
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